1. Field of the Invention
This invention relates in general to golf clubs and more particularly to the type of golf clubs known as irons with these iron golf clubs having improved performance characteristics resulting from strategic changes in weight distribution.
2. Description of the Prior Art
Although a golfer controls the swinging of a golf club, at the moment of impact the club head acts as though it were a free mass moving at a particular velocity. Most of the energy of this moving mass is transferred to the golf ball in about half of a millisecond with the result being that the ball, which is compressed against the face of the club, will spring clear as it returns to its spherical configuration. Maximum energy transfer and desirable golf ball flight direction and trajectory are achieved when the golf club head impacts a golf ball on the "sweet spot" of the club. The sweet spot of a golf club head is a point on the face of the club head which is in general alignment with the center of gravity of the golf club.
It is very difficult even for highly skilled and experienced golfers to consistently impact a golf ball on the sweet spot of a golf club, and when the sweet spot is missed the golf club will tend to twist, i.e., the face of the club will move from a position of being square with the intended flight path of the ball. When this happens, the amount of energy transferred to the golf ball will be less than maximum which results in a loss of distance. Also such twisting, or turning, of the golf club face will cause the golf ball to deviate from an ideal flight path.
To minimize the effects of mis-hitting a golf ball, modern golf club design has produced a class of game improvement golf clubs which are sometimes referred to as cavity back, or perimeter weighted clubs. As the name suggests, such clubs are formed with a central hollow, or cavity, in the back surface thereof, and the metal which would otherwise be located in the cavity is redistributed in predetermined proportions to strategic locations on the club heads. A relatively large mass is concentrated in the sole of these game improvement clubs to lower the center of gravity. This makes it easier for a golfer to get the center of gravity of the club head below the center of gravity of a golf ball at the moment of impact for producing a properly airborne and solidly hit ball. In addition, relatively large concentrations of mass are located in the heel and toe areas of the cavity back club to minimize the effects of hitting a golf ball on the toe or heel of the club head. When toe or heel hits occur, the club head will twist about the center of gravity. Such twisting, as mentioned above, results in less than a maximum transfer of energy to the golf ball at impact and deviations from the intended flight path of the ball will occur. By designing the golf club head with relatively large concentrations of mass in the toe and heel areas of the club head, the moment of inertia is increased so that the golf club will resist twisting movements in response to laterally off-center hits, i.e., in the directions of the toe and heel of the club head.
Many prior art golf clubs have been designed with mass concentrations in the sole, toe and heel areas of the club head in attempts to achieve optimum weight distribution benefits. The degree of success in achieving these design objectives varies from one club head to another in that the club's performance relies, along with other design parameters, on the proportions of the mass concentrations and the locations of those concentrations.
In a prior art design of mine, which is fully disclosed in U.S. Pat. No. 4,621,813, I removed metal from the central area at the back edge of the sole of the golf club head where it forms a junction with the lower edge of the back surface thereof. The removed metal was relocated to strategic areas in the toe and heel portions of the club head. This redistribution of material resulted in improved resistance to twisting as a result of lateral mis-hitting of the club, i.e., in the direction of the hoe or heel of the club and this improvement was made without any change in the total weight of the club head. Further, this improvement was made without sacrificing any other desirable characteristics of the golf club in that the relocated material was taken from a non-crucial area of the golf club head.
In most modern golf club designs, including mine as set forth in the hereinbefore disclosed U.S. Patent, considerably more than half of the golf club head mass is located in the lower part of the golf club head. As described above, the reason for this is to take advantage of the benefits derived from toe and heel mass concentrations and sole weighting. I have found that although minimizing the effects of mis-hits in the direction of the toe or heel of the club head is a major consideration in the design of the golf club heads, the effects of mis-hits in vertical directions relative to the center of gravity should not be overlooked.
As is the case with twisting movements of the club head resulting from mis-hits in the direction of the toe or heel, the club head will react to mis-hits in vertical directions by movements that may be described as tilting or tipping movements. When the impact point of the golf ball on the face of the club head is high on the face, i.e., above the sweet spot, that impact causes the club head to tilt about the center of gravity and such tilting will be in a direction which increases the loft angle of the club. This occurs due to the inertia of the mass concentration at the sole of the club head which causes the lower end of the club head to move forwardly under the ball in an arcuate path about the center of gravity. This movement is amplified by the relative lack of mass in the upper end of prior art golf clubs which results in a relatively small moment of inertia that provides very little resistance to tilting motion.
Similarly, when the impact point is low on the face of the golf club head, i.e., below the sweet spot, the lack of mass in the upper end of the club head provides a small moment of inertia and thus a very low resistance to tilting of the golf club head in a direction that reduces the loft angle of the club. In other words, the top end of the golf club head moves forwardly over the top of the ball in an arcuate path about the center of gravity.
To the best of my knowledge, no prior art golf clubs have been designed to provide mass concentration in the top part of iron type golf club heads with those concentrations being located and of sufficient magnitude to effectively minimize the hereinbefore described tilting problem.
A particular prior art golf club design is disclosed in U.S. Pat. No. 5,011,151 which issued to Anthony J. Antonious on Apr. 30, 1991. The club head disclosed in this patent had some of the mass, which is referred to as toe counterweight, located above a theoretical longitudinal axis of the club head. The longitudinal axis is defined as bisecting the face of the club head and is shown as extending between the heel and toe of the club head. The toe counterweight is a relatively large mass concentration which blends smoothly with the mass of the sole so that the counterweight appears to be an upwardly sweeping extension of the sole. At least 25% and preferably 33% of the mass of the toe counterweight is disclosed as being located above the longitudinal axis to shift the center of gravity upwardly and toward the toe which maximizes the energy transfer when a golf ball is hit off-center toward the toe. Although the design of this prior art golf club appears to provide improved resistance to the club tilting problem, it is believed that less than the maximum benefit is achieved in that the toe counterweight does not extend all the way to the top of the toe but ends abruptly at a point below the top. This golf club design is further disclosed as having the top ridge at the upper end of the club of increased mass to provide a top counterweight. However, the cross-sectional configuration of the top ridge is of substantially rectangular conventional design and does not derive the maximum benefit from the mass located in that area.
Therefore, a need exists for a new and improved set of golf clubs which are configured to minimize the tilting motion of the club heads resulting from vertically miss-hit golf balls, and to otherwise provide a club head design with overall improvement of the club head balance.